Evaluation of radiograph parameters used to assess prosthetic overlengthening in radial head arthroplasty

Radiographic landmarks, such as the lateral ulnohumeral joint space (LUHJ) and the proximal edge of the lesser sigmoid notch (SN), are intra-operative parameters used to evaluate radial head prosthetic overlengthening. This study aims to evaluate the reliability of the LUHJ and SN as radiographic parameters to assess radial head prosthetic overlengthening. We hypothesize that the SN is a more reliable radiographic landmark compared with the LUHJ for diagnosing prosthetic radial head overlengthening.

Radial head prosthetics were implanted into cadaver upper extremities at 0, +2, +4, and +6 mm. Radiographs were obtained with the cadaver positioned in full extension. The radiographs were then randomized and presented to 4 fellowship-trained upper extremity orthopedic surgeons to evaluate for prosthetic overlengthening. Following data collection, the inter-rater and intra-rater reliability of the 2 radiographic parameters at each position were calculated using Fleiss and Cohen κ.

The inter-rater reliability of the SN was greater than that of the LUHJ (κ = 0.55 vs. 0.43), and the intra-rater reliability was higher for the SN than for the LUHJ (0.54 vs. 0.48). The SN had fair to moderate intra-rater reliability at full extension (κ = 0.54). The LUHJ had fair to moderate intra-rater reliability at full extension (κ = 0.48).

Neither radiographic landmark is sufficiently reliable to adequately assess radial head prosthetic overlengthening, underscoring the need for the surgeon to consider multiple factors and to ensure proper elbow positioning during radiographic evaluation of prosthetic length.